I have yet to see a solution to that type of thing though as every config language exists on a spectrum of syntax to full blown programing language.
It does get a lot easier to deal with when you have VS Code tied into CRD definitions for example, butcimmnot convinced config is the problem so much as just Kubernetes is all things to all people and as a result what any given configuration actually does is almost completely random and likely to hit a bunch of edge cases.
My choice is "whatever is available in the standard library" - which used to be INI, JSON or YAML. But with python 3.11 there is also TOML, which is nice...
*Honorable mention to Nix, which is also functionally a configuration language, released a decade before those. Feel like recent few years there has been an increase in remaking existent things slightly different and marketing them like new.
Speaking of which, Pkl looks absolutely fascinating, I might have to check that out...